INTRODUCTION TO AN ALGEBRAIC THEORY OF ARROWS, II. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 82, n. 1, p. 63–117, 1991. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/523. Acesso em: 12 jan. 2026.